1. Field of the Invention
The present invention relates generally to network switches and, more particularly, to a system and method for achieving lossless packet delivery in packet rate oversubscribed systems.
2. Introduction
Increasing demands are being placed upon the data communications infrastructure. These increasing demands are driven by various factors, including the increasing bandwidth requirements of multimedia traffic. To accommodate the increasing bandwidth requirements, communication link speeds have also continued to evolve. For example, 10 Gigabit Ethernet (GbE) ports are commonly used for I/O on many of today's network switches.
One of the problems introduced by the increasing I/O bandwidth exemplified by the 10 GbE port is the potential for an oversubscribed switch. In general, an oversubscribed condition for a switch can occur when the combined I/O bandwidth across a set of ports exceeds the core bandwidth of the switch. Some of today's switches have designed configurations that have the potential for entering into an oversubscribed condition. This results from the need for significant I/O bandwidth for a port, faster time to market, and a low likelihood that all of the I/O ports will receive traffic at the highest capacity at the same time.
When a switch enters into an oversubscribed condition where the packet arrival rate exceeds the packet processing rate, oversubscription buffers limits can be exceeded. When the oversubscription buffer limits are exceeded, the oversubscription buffer backs up and packet loss can occur. It should be noted that an oversubscribed switch may continue to support the line rate as long as the average packet size for a specified period of time exceeds a predefined packet size. For example, if the average packet size is greater than 150 bytes for all periods of time greater than one second, then packet loss will not occur.
For some classes of traffic, packet loss can produce little to no impact on network services and applications. In data-center applications, however, packet loss can be unacceptable. What is needed therefore is a mechanism that achieves lossless packet delivery in packet rate oversubscribed systems.